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In order to reduce our dependance on fossil fuels, the development of technologies for green energy production is of major interest. Hydrothermal gasification process (SCWG) is a promising technology for producing an energetic gas from organic waste with high moisture content. By bringing the feedstock to high temperatures and pressures (T>374 °C; P>221 bar), the water it contains becomes supercritical and assists in the conversion of the organic content of the feedstock. Under these conditions, water acts as both non-polar solvent and as a reagent, enabling the conversion of the organic content into an energy-rich gas mainly composed of H2, CH4 and CO2. At the end of the process, a carbon-depleted water is returned. The inorganic content of the feedstock precipitates in supercritical water and can be recovered using appropriate technological solutions. High operating temperature (T>600 °C) is required to ensure almost total conversion, which can reduce the overall energy efficiency of the process and cause severe damages to the process unit materials. The use of heterogeneous catalysts is a solution that allows to reduce the operating temperature (T<450 °C), but requires the use of catalyst in harsh conditions. Sugar beet vinasse was chosen as the biomass waste for this thesis work. this effluent is generated by sugar industries that produce ethanol by distilling a mixture of fermented beet sugar. This vinasse is currently used as a potassium fertilizer, therefore non-valorizing its organic content. Its too high potassium content makes it unsuitable for biogas production by conventional methanization. SCWG appears as a suitable solution to valorize sugar beet vinasse, allowing both gas production from its organic content and inorganics recovery for fertilizers production. In this work, a complete study on vinasse valorization through SCWG processing was carried out by monitoring gas products and intermediary compounds concentration in the aqueous phase. There are very few references regarding this vinasse valorization in the literature. After complete characterization of the vinasse, a first set of non-catalytic experiments was conducted in batch reactor. The influence of temperature, which is the main operating parameter affecting the gasification results, was studied. The catalytic SCWG of vinasse in batch reactor was then studied using Raney nickel as a reference catalyst. The different conditions including various catalyst loadings and operating temperatures allowed to distinguish different reaction pathways, differing from the observations made in the non-catalytic experiments. Tests with model compounds were also performed to observe different behaviors of the main constituents of the vinasse. The synthesis of heterogenous catalysts was an important part of this work, enabling the study of the catalytic material under SCWG conditions. Several nickel catalysts supported on metal oxides were synthesized, characterized and used in SCWG of vinasse. These experiments and the focus on the catalytic material highlighted the impact of SCWG operating conditions on catalyst deactivation. Synthesis strategies and catalyst management in the batch reactor allowed to increase catalyst stability and activity. Finally, SCWG tests were performed in continuous-flow reactor, with and without synthesized catalyst utilization. These experiments provide insight into the major technological barriers inherent in the valorization of a complex feedstock such as vinasse by catalytic SCWG.